Liquid sampling utilizing ribbed pipette tip for barrier penetration

Abstract

An apparatus and method for liquid sampling utilizing a ribbed pipette tip for barrier penetration is disclosed herein. The unique, disposable plastic pipette tip of the present invention has an outer surface with at least three ribs extending longitudinally along the outer surface of the barrel. Each rib is circumferentially spaced from one another at a uniform distance, with each rib being symmetrically sized and positioned on the pipette tip barrel. The pipette tip is capable of being placed on a mounting shaft of a hand-held pipette or on the mounting head of an automated liquid handling machine. The pipette tip is rigid and straight enough to pierce a barrier sheet or resilient barrier sealing a container holding a liquid to be sampled. The ribs of the pipette tip operate to keep the barrier separated from the outer surface of the pipette tip such that ambient air is allowed to flow into and from the interior of the sealed container assembly during aspiration of the liquid sample into the pipette tip allowing for accurate transfer of liquids while minimizing the risk of contamination. The pipette tip and method of the present invention may be utilized in an automated pipetting system to sample an array of sealed containers, such as sealed wells and the pipette tip is sufficiently. The pipette of the present invention may include a self-sealing filter to prevent cross-contamination.

1 . A method of sampling a liquid sample from a sealed container assembly using a disposable, plastic pipette tip, the method comprising the steps of: 
 a) providing a liquid sample in a sealed container assembly comprising a container having a closed bottom portion and a top portion with an open end, the liquid sample being contained in the bottom portion of the container, and a closure associated with the top portion of the container that seals the open end of the container, the closure comprising at least in part a barrier sheet that separates an interior of the container from the ambient environment;    b) providing a disposable, plastic pipette tip comprising a hollow body having a proximal opening at its proximal end for mounting to a mounting shaft of a pipettor and a distal opening at its distal end for aspirating liquid into and dispensing liquid from the hollow body, the hollow body comprising a collar encircling and extending from the proximal opening, and a barrel extending from the collar to the distal opening, the barrel having an outer surface with at least one rib extending longitudinally along the outside surface of the barrel;    c) placing the recited pipette tip on a mounting shaft of a pipettor;    d) piercing the barrier on the container assembly closure with the distal end of the pipette tip barrel and moving the barrel through the barrier such that a rib of the pipette tip radially shears the barrier outwardly from a location where the distal end of the pipette tip pierced the barrier sheet and continuing to move the barrel through the barrier until the distal opening is submerged in the liquid sample in the sealed container assembly;    e) aspirating liquid sample from the container into the pipette tip through the submerged distal opening;    f) while aspirating the liquid specimen into the pipette tip, using a rib on the pipette tip barrel to spread the pierced opening in the barrier such that ambient air is able to flow into and from the interior of the sealed container assembly during aspiration of the liquid sample into the pipette tip; and    removing the pipette tip containing the aspirated liquid sample from the container assembly.    
   
   
       2 . The method recited in  claim 1  wherein at least  3  ribs extend along the outside surface of the barrel and each longitudinal rib on the barrel is circumferentially spaced from each additional rib around the outer surface of the barrel at a uniform distance from each other, and each rib is symmetrically sized and positioned on the pipette tip barrel.  
   
   
       3 . The method recited in  claim 1  wherein a central longitudinal axis passes through the hollow body of the pipette tip and an edge of the barrel defining the distal opening lies in a plane perpendicular to the central longitudinal axis.  
   
   
       4 . The method as recited in  claim 1  wherein a central longitudinal axis passes through the hollow body of the pipette tip, each rib has an apex, and the distance from the central longitudinal axis to the apex of each rib is such that an imaginary line passing through the apex to an adjacent apex in a plane perpendicular to the central longitudinal axis does not otherwise intersect the outer surface of the pipette barrel.  
   
   
       5 . The method recited in  claim 1  wherein a central longitudinal axis passes through the hollow body and the barrel has an upper barrel portion adjacent the collar and a lower barrel portion adjacent the distal opening, the upper barrel portion being in the shape of a truncated cone, the lower barrel portion being in the shape of an elongated cone in which the diameter of the hollow body tapers smaller at a lower rate with respect to longitudinal central axis than the upper barrel portion, and each rib extends longitudinally along the barrel from the lower portion to the upper portion.  
   
   
       6 . The method recited in  claim 5  wherein each rib extends longitudinally completely to the distal opening, and wherein the thickness of each rib as measured away from the outer barrel surface tapers as it approaches the distal opening so that the thickness of each respective rib from the barrel surface converges to zero as the rib approaches the edge of the barrel defining the distal opening.  
   
   
       7 . The method recited in  claim 5  wherein the thickness of each rib as measured away from the outer barrel surface tapers and converges to zero as it approaches the collar portion.  
   
   
       8 . The method recited in  claim 1  wherein the pipette tip further comprises a filter located in the hollow body of the pipette tip.  
   
   
       9 . The method recited in  claim 8  wherein the filter is a self-sealing filter.  
   
   
       10 . The method recited in  claim 1  wherein the collar extends along the hollow body of the pipette tip away from the proximal opening and at least a portion of an inside surface of the collar provides a seal when the pipette tip is mounted on the pipettor and an outer surface of the collar comprises a plurality of ribs.  
   
   
       11 . The method recited in  claim 1  wherein a central longitudinal axis passes through the hollow body of the pipette tip and at least a portion of an outer surface of the collar extends along the hollow body from the proximal opening towards the distal opening until reaching a shoulder that connects the outer surface of the collar to the outer surface of the barrel, the shoulder being substantially perpendicular to the longitudinal central axis.  
   
   
       12 . The method recited in  claim 1  wherein the recited container is a well in a well plate having an array of wells, and the recited closure is a non-resilient foil barrier sheet covering the array of wells.  
   
   
       13 . The method recited in  claim 1  wherein the recited container is a well in a well plate having an array of wells, and the recited closure is a non-resilient film barrier sheet covering the array of wells.  
   
   
       14 . The method recited in  claim 1  wherein the recited container is a cluster tube and the recited barrier sheet comprises non-resilient foil.  
   
   
       15 . The method recited in  claim 1  wherein the recited container is a cluster tube and the recited barrier sheet comprises non-resilient film.  
   
   
       16 . A method of sampling a plurality of liquid samples each contained in one of a plurality of sealed container assemblies with a plurality of disposable, plastic pipette tips, the method comprising the steps of: 
 a) providing a plurality of liquid samples each in a sealed container assembly, the sealed container assemblies being arranged in columns and rows to form a two dimensional array, each sealed container assembly comprising a container having a closed bottom portion and a top portion with an open end, the respective liquid sample being contained in the bottom portion of the respective container, and a closure associated with the top portion of each container and sealing its open end, the closure comprising at least in part a barrier sheet that separates an interior of the container from the ambient environment;    b) providing a plurality of disposable, plastic pipette tips each comprising a hollow body having a proximal opening at its proximal end configured to be mounted on the mounting shaft of an automated pipetting system configured to accept an array of pipette tips and a distal opening at its distal end for aspirating liquid into and dispensing liquid from the hollow body, the hollow body comprising a collar encircling and extending from the proximal opening, a barrel extending from the collar to the distal opening, the barrel having an outer surface with at least one rib extending longitudinally along the outside surface of the barrel;    c) mounting a plurality of the recited pipette tips in an array on the mounting head for an automated pipetting system;    d) contemporaneously piercing at least a portion of the barrier sheets on the array of container assemblies with the distal end of at least some of the mounted pipette tips and moving the barrel of the pipette tips through the respective barrier sheets such that a rib radially shears the barrier outwardly from a location where the distal end pierced the barrier sheet and continuing to move the barrel through the barrier until the tip openings at the distal ends of the pipette tips are submerged in the liquid samples in the respective sealed container assemblies;    e) aspirating the liquid samples into the respective pipette tips through the submerged distal openings;    f) while aspirating the liquid specimens into the respective pipette tip, using a rib on the pipette tip barrel to spread the pierced opening in the respective barrier sheets such that ambient air is able to flow into and from the interior of the respective sealed container assembly during aspiration of the sample into the pipette tip; and    g) removing each respective pipette tip containing aspirated liquid sample from the respective container assembly.    
   
   
       17 . The method recited in  claim 16  wherein at least 3 ribs extend along the outside surface of the barrel and each longitudinal rib on the barrel of the pipette tips is circumferentially spaced from each additional rib around the outer surface of the barrel at a uniform distance from each other, and each rib is symmetrically sized and positioned on the pipette tip barrel.  
   
   
       18 . The method recited in  claim 16  wherein a central longitudinal axis passes through the hollow body of the pipette tips and an edge of the barrel defining the distal opening lies in a plane perpendicular to the central longitudinal axis.  
   
   
       19 . The method as recited in  claim 16  wherein a central longitudinal axis passes through the hollow body of the pipette tips, each rib has an apex, and the distance from the central longitudinal axis to the apex of each rib is such that an imaginary line passing through the apex to an adjacent apex in a plane perpendicular to the central longitudinal axis does not otherwise intersect the outer surface of the pipette barrel.  
   
   
       20 . The method recited in  claim 16  wherein a central longitudinal axis passes through the hollow body and the barrel has an upper barrel portion adjacent the collar and a lower barrel portion adjacent to distal opening, the upper barrel portion being in the shape of a truncated cone, the lower barrel portion being in the shape of an elongated cone in which the diameter of the hollow body tapers smaller at a lower rate with respect to longitudinal central axis than the upper barrel portion, and each rib extends longitudinally along the barrel from the lower portion to the upper portion.  
   
   
       21 . The method recited in  claim 19  wherein each rib extends longitudinally completely to the distal opening, and wherein the thickness of each rib as measured away from the outer barrel surface tapers as it approaches the distal opening so that the thickness of each respective rib from the barrel surface converges to zero as the rib approaches the edge of the barrel defining the distal opening.  
   
   
       22 . The method recited in  claim 19  wherein the thickness of each rib as measured away from the outer barrel surface tapers and converges to zero as it approaches the collar portion.  
   
   
       23 . The method recited in  claim 16  wherein the pipette tips further comprise a filter located in the hollow body of the pipette tips.  
   
   
       24 . The method recited in  claim 23  wherein the filter is a self-sealing filter.  
   
   
       25 . The method recited in  claim 16  wherein the collar extends along the hollow body of the pipette tips away from the proximal opening and at least a portion of an inside surface of the collar provides a seal when the pipette tips are mounted on the mounting head and an outer surface of the collar comprises a plurality of ribs.  
   
   
       26 . The method recited in  claim 16  wherein a central longitudinal axis passes through the hollow body of the pipette tip and at least a portion of an outer surface of the collar extends along the hollow body from the proximal opening towards the distal opening until reaching a shoulder that connects the outer surface of the collar to the outer surface of the barrel, the shoulder being substantially perpendicular to the longitudinal central axis.  
   
   
       27 . The method recited in  claim 16  wherein the recited container is a well in a well plate having an array of wells, and the recited closure is a non-resilient foil barrier sheet covering the array of wells.  
   
   
       28 . The method recited in  claim 16  wherein the recited container is a well in a well plate having an array of wells, and the recited closure is a non-resilient film barrier sheet covering the array of wells.  
   
   
       29 . The method recited in  claim 16  wherein the recited container is a cluster tube and the recited barrier sheet comprises non-resilient foil.  
   
   
       30 . The method recited in  claim 16  wherein the recited container is a cluster tube and the recited barrier sheet comprises non-resilient film.